1. Field of the Invention
The present invention relates to a method for reinforcing an existing wall structure, and preferably for reinforcing a ferroconcrete wall type pier or the like.
2. Description of the Prior Art
Known methods for reinforcing existing ferroconcrete piers include steel lining methods and concrete lining methods. Further, a method using steel segments has been disclosed by the present applicant in Japanese Laid Open Patent Publication No. JP-9,209,580.
The method using steel segments will be described with reference to FIGS. 8a and 8b. This method employs: a plurality of PC steel bars 3 inserted into a plurality of holes which are pierced through an existing wall type pier 2, in the direction of its thickness, installed on a bridge pedestal 1; and a plurality of steel segments 4, each of which are formed into a column having a cross-section in the shape of a circular-arc, and which are integrally provided with connecting flanges 4a at both sides of each circular-arc column in the width direction. Several stages of steel segments 4, which are arranged adjacent to each other sideways, are vertically arranged onto the wall surface of the pier 2 by superimposing the respective flanges 4a. The PC steel bars 3 are allowed to pass through a plurality of holes formed in the flanges 4a and the holes of the pier 2. The end portions of the PC steel bars 3 are then screwed, and the steel segments 4 are fixed onto the wall surface. Then, concrete 5 is placed into the circular-arc-like space between the steel segments 4 and the wall surface, and the steel segments 4 are integrated to the wall surface of the pier 2. The PC steel bars 3 are then tensioned to impart restricting force to the concrete.
Since a plurality of steel segments is divided in the vertical and horizontal direction, this method is applicable to a pier having any cross-section.
Compared with the steel lining method and the concrete lining method, the segment method is simple in structure, realizes a larger concrete restricting effect, and increases earthquake-resistance ability. The segment method also eliminates the necessity of providing a form required for the concrete lining method, thereby achieving labor-saving of construction and shortening of construction period.
FIG. 8a shows an example in which two pieces of the PC steel bars are provided for each steel segment; FIG. 8b shows an example in which three pieces of the PC steel bars are provided for each steel segment.
The above-described segment method, however, has the following technical problems.
The restricting force applied in the axial direction of the pier, that is, to the wall surface, becomes large by provision of the steel segments and the PC steel bars, and a sufficient earthquake-resistance ability of the wall surface is obtained. However, since the side surfaces (end surfaces) of the pier, which are located in the direction perpendicular to the axial direction, are not treated, when a large vibration is applied to the side surfaces of the pier, the covering concrete on the side surfaces is extruded by buckling of the main reinforcement, and damages progress therefrom. Therefore, not only is the earthquake-resistance ability decreased, but also the appearance is harmed.
Further, since the steel segments are divided into a plurality in the horizontal direction, there is a limitation in introducing the restricting force. This also complicates both the operation to superimpose the flanges onto each other, and the crane operation for carrying the divided steel segments upon actual assembly thereof.